Yes. The electrets just don't require bias, as their diaphragm has a permanent charge, so the bias pin on the connector isn't connected to anything. They do this by casting the film in the presence of an extremely strong electrical field.
Because the film is cast, it's nowhere near as thin as you can get with 'stats that have external bias voltage. It also has to be a polymer that has polar molecules.
Sometimes people say that electret films can "lose their charge" which is preposterous. The polymers used have positive and negative ends to their chains, and that polarity is a function of the physical properties of the atoms and the molecular structure - the electret "charge" is a matter of aligning the molecules, nothing else. So exactly what would cause the film to "lose" that charge? Physically rotating the molecules? But they are susceptible to damage like any other transducer, and like i said, Sony proposed that a charge can build up between the stators and film that can't be drained off if the film is electrically isolated.
The SRD-4 and most SRD-6 have the exact same transformers in them. Mine certainly do, though my SRD-6 has some extra mounting holes to support larger transformers. They just cut the center tap wire off of the transformers in the SRD-4, since there's no bias to reference to it.